Robust optical readout and characterization of nuclear spin transitions in nitrogen-vacancy ensembles in diamond

At a Glance

Metadata	Details
Publication Date	2020-04-28
Journal	Physical Review Research
Authors	A. Jarmola, I. Fescenko, V. M. Acosta, M. W. Doherty, F. K. Fatemi
Institutions	GSI Helmholtz Centre for Heavy Ion Research, Helmholtz Institute Mainz
Citations	21
Analysis	Full AI Review Included

Executive Summary

High-Contrast Optical Readout: Achieved direct optical readout of ¹⁴N nuclear spin transitions in NV ensembles with a maximum Rabi oscillation contrast (C) of ~3.8%. This contrast is comparable to that typically realized with NV electron spins.
Enhanced Robustness: The technique utilizes direct optical detection near the Excited-State Level Anticrossing (ESLAC), eliminating the need for microwave mapping pulses, thereby increasing the robustness against magnetic field and temperature fluctuations.
Minimal Thermal Sensitivity: The temperature dependence of the nuclear quadrupole coupling constant Q (d|Q|/dT = -35.0 Hz/K at 297 K) is approximately 2000 times smaller than the corresponding dependence of the electron spin zero-field splitting D.
Quantum Sensing Advantage: The combination of high readout contrast and extremely low thermal sensitivity makes ¹⁴N nuclear spins ideal candidates for precision quantum sensing applications, particularly rotation sensing (gyroscopes).
Material Characterization: Precise determination of fundamental constants: Q = -4.9457(3) MHz and the ¹⁴N nuclear gyromagnetic ratio (γ_n) = 307.5(3) Hz/G.
Coherence Time: Measured nuclear spin coherence time (T₂^*) is in the range of 0.5 to 0.8 ms, which is 10³-fold longer than typical electron spin coherence times.

Technical Specifications

Parameter	Value	Unit	Context
Max Nuclear Rabi Contrast (C)	3.8	%	Observed at B ~ 485 G
High Contrast B Field Range	450 to 550	G	Range where C > 2%
Quadrupole Coupling Temp Slope (d	Q	/dT)	-35.0(2)
Electron ZFS Temp Slope (dD/dT)	-74.2(7)	kHz/K	For comparison (~2000x higher)
Nuclear Quadrupole Constant (Q)	-4.9457(3)	MHz	Derived from Ramsey spectroscopy
Nuclear Gyromagnetic Ratio (γ_n)	307.5(3)	Hz/G	Derived value for ¹⁴N NV
Nuclear Spin Coherence Time (T₂^*)	0.5 to 0.8	ms	Across all tested T and B ranges
Laser Wavelength	532	nm	Optical excitation
Laser Power / Pulse Duration	20 mW / 20 µs	N/A	Used for optical excitation
Electron Irradiation Dose	~10¹⁸	cm^-2	NV center creation
Annealing Temperature / Time	800 °C / 3 hours	N/A	Post-irradiation processing
Magnetic Field Range Tested	350 to 675	G	Experimental range
Temperature Range Tested	77.5 to 420	K	Experimental range

Key Methodologies

Diamond Sample Preparation:
- Used a [100]-cut High-Pressure High-Temperature (HPHT) grown diamond.
- Initial nitrogen concentration was approximately 50 ppm.
- NV centers were created by irradiation with 10 MeV electrons at a dose of ~10¹⁸ cm^-2.
- Subsequent annealing was performed in vacuum at 800 °C for three hours.
Experimental Setup:
- Measurements conducted using a custom-built confocal microscopy setup.
- Sample mounted inside a continuous flow microscopy cryostat for temperature control (77.5 K to 420 K).
- Static magnetic field (B) applied along the NV axis using a neodymium permanent magnet mounted on a three-axis translation stage.
Measurement Techniques:
- ODNMR Spectroscopy: Used to observe nuclear spin transitions (f₁ and f₂) and confirm strong nuclear polarization into the |0, +1> state.
- Rabi Oscillations: Measured using a radio-frequency (RF) pulse sequence (Fig. 2c) to determine the optical readout contrast (C) as a function of magnetic field.
- Ramsey Interferometry: Employed a π/2-τ-π/2 pulse sequence (Fig. 3a,b) to precisely measure the nuclear spin transition frequencies (f₁ and f₂) as a function of temperature and magnetic field, and to infer the coherence time T₂^*.
Readout Mechanism:
- Direct optical readout of the nuclear spin state, relying on nuclear-spin-dependent fluorescence near the Excited-State Level Anticrossing (ESLAC) region (~500 G).
- Fluorescence was collected through a 650-800 nm bandpass filter.

Commercial Applications

Quantum Sensing and Metrology: Provides a foundation for developing next-generation quantum sensors utilizing the robust properties of nuclear spins.
Inertial Navigation (Gyroscopes): The primary target application. The minimal temperature and magnetic field sensitivity of the ¹⁴N nuclear spin transitions are critical for high-precision rotation sensing.
High-Stability Clocks: The reduced environmental sensitivity of the nuclear quadrupole coupling constant Q suggests potential for use in highly stable frequency references or clocks.
Quantum Information Processing (QIP): The long coherence time (T₂) of the nuclear spins makes them promising candidates for robust quantum memory elements in diamond-based QIP architectures.
Thermometry and Magnetometry: Although the nuclear spin is less sensitive to magnetic fields, the NV platform itself is a leading technology for high-resolution thermal and magnetic field mapping.

View Original Abstract

Nuclear spin ensembles in diamond are promising candidates for quantum sensing applications, including rotation sensing. Here we characterize the optically detected nuclear spin transitions associated with the N-14 nuclear spin within diamond nitrogen-vacancy (NV) centers. We observe that the contrast of the nuclearspin-dependent fluorescence is comparable to the contrast of the NV electron-spin-dependent fluorescence. Using Ramsey spectroscopy, we investigate the temperature and magnetic field dependence of the nuclear spin transitions in the 77.5-420 K and 350-675 G range, respectively. The nuclear quadrupole coupling constant Q was found to vary with temperature T, yielding d vertical bar Q vertical bar/dT =-35.0(2) Hz/K at T = 297 K. The temperature and magnetic field dependencies reported here are important for quantum sensing applications such as rotation sensing and potentially for applications in quantum information processing.

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevresearch.2.023094